Many household appliances provide an audio signal to alert the owner to the need to take timely action. For example, many dryers have an “end of cycle” audible signal that is activated when the drying cycle has been completed so that the user may remove clothes before wrinkles “set”. This signal is normally provided by high voltage (110-120 volts) electromechanical “buzzer”. Such buzzers provide a relatively harsh single tone, the latter limiting their use to conveying one type of information.
High-end refrigerators providing microprocessor control circuits may monitor whether the refrigerator door is fully closed and sound a tone when the door is left ajar by a small amount that might otherwise go unnoticed. Such failure of the refrigerator door to seal wastes energy, causes condensation, and can affect the condition of the food. These refrigerators may provide the warning tone using a small piezoelectric audio transducer driven by the low voltage microprocessor circuitry. Modulation of the tone using software executed by the microprocessor can provide for a tone that is both distinctive and pleasant sounding. Modulation of the tone can allow multiple different conditions to be signaled.
The use of a modulated audio transducer, such as a piezoelectric transducer, to provide an alert to the appliance owner has not been adopted widely in lower end appliances or appliances that do not normally include a microprocessor controller, primarily because the incremental cost of such transducers, including the necessary low-voltage power source, interconnecting wiring and support circuitry, cannot be cost justified despite the desirability of modulated audio for aesthetic and functional purposes.